1. Field of the Invention
The present invention relates to a printer having a heating processor which processes a printed medium by heating after characters or patterns are printed on the printing medium by a printing means.
2. Description of the Related Art
An ink jet printer is known which prints characters or patterns on a printing medium with the use of a hot-melt ink, which is a solid at a normal temperature and is melted by heating, and an ink jet printer head. In the case of the ink jet printer, it is possible to print not only on ordinary printing paper but also on a transparent overhead projector film (hereinafter referred to as an OHP film) made of resin to be used for the projection of characters or patterns with an overhead projector. The quantity of jetted ink per dot from an ink jet printer head is very small and its heat capacity is also very small, so that as soon as it sticks on a printing medium it is deprived of heat and hardened. Because of this, the ink is upheaved on the printing surface of a printing medium and the printing surface is rendered uneven. When a printing medium is ordinary printing paper, such unevenness is not a problem. When a printing medium is an OHP film, the convex of ink is very noticeable and the ink is hardened to have a form close to that of a convex lens, which causes a problem as described in the following. An OHP film printed with multicolored inks is often used in an overhead projector and a printed image is projected on a screen being enlarged. When an ink is hardened on the OHP film in a form similar to a convex lens, light is refracted by the ink having a similar form to a convex lens, and distinct colors cannot be projected on a screen. In order to solve such a problem, an image forming method as disclosed in U.S. Pat. No. 4,853,706 has been invented. In the invention, an OHP film is thermally processed on which characters or patterns are printed and the inks are hardened. The inks heated to a temperature higher than the melting point are melted on the OHP film and transformed to an approximately flat form from an approximately convex lens shaped form.
For performing a heating process of an OHP film after it is printed with an ink jet printer, a heating processor has to be prepared separately. In this case, if an OHP film output from an ink jet printer is inserted into a heating processor manually, there can be a problem that the OHP film may be inserted upside down into the heating processor, or fingerprints may be left on the OHP film. Therefore, when an OHP film is to be printed, it is desirable to use an ink jet printer having a built-in heating processor. In other words, for an OHP film it is ideal to perform a series of processes, from printing to a heating process, inside an ink jet printer.
An ink jet printer having a built-in heating processor is proposed. In the ink jet printer, printing is performed on an ordinary printing paper and an OHP film
and, as described above, a heating process is necessary for an OHP film and not for ordinary printing paper. In the ink jet printer, there is provided a sensor for determining whether a printing medium is an ordinary printing paper or an OHP film, and whether a heating process is to be performed or not is decided according to the kind of printing medium. Still, there can occur a problem in an ink jet printer in which whether a heating process is necessary or not is decided only by the kind of a printing medium being used. In short, the problem is that a heating process is necessarily performed whenever printing is performed on an OHP film. Thus, in the printing on an OHP film there is a case where a heating process is not needed. When an OHP film is printed with a black ink only, for example, there is no problem in color in the case of projection, so that the heating process is not always needed. Even in a case of color printing on an OHP film, if the printing is a test printing for confirming the printed result, a heating process is not needed. When a heating process is performed, it requires a comparatively long printing time, and also the electric power for a heating process is additionally needed, which raises printing cost. Moreover, printing media are not limited to so simple ones as to be classified into transparent ones and opaque ones. In addition, there are translucent ones such as tracing paper, for example. When the kind of a printing medium is judged by the light transmission of the printing medium, a translucent printing medium as mentioned in the above can be judged as an OHP film, and it can be heat-processed erroneously.